1. Field of the Invention
The present invention relates to a zoom lens system for a compact camera, and in particular, relates to a focusing operation thereof.
2. Description of the Related Art
In a zoom lens system for a compact camera, there is no need to provide a long back focal distance, unlike a zoom lens system for a single lens reflex (SLR) camera which requires a space for providing a mirror behind the photographing lens system. Accordingly, a compact camera generally employs a telephoto type lens system in which positive and negative lens groups are provided in this order from the object, while a SLR camera generally employs a retrofocus type lens system in which negative and positive lens groups are provided in this order from the object.
In a compact camera employing a telephoto type lens system, there has been a demand, in recent years, for a higher zoom ratio in a zoom lens system. In order to respond to this demand, a three-lens-group zoom lens system has been frequently employed. In such a three-lens-group zoom lens system, the three lens groups independently move along the optical axis upon zooming. On the other hand, focusing is performed by moving one of the lens groups, usually the first or second lens group, along the optical axis. In order to attain miniaturization of the three-lens-group zoom lens system, reducing the overall length, the lens diameters thereof, and the thickness of the lens groups are all important factors. However, if the number of lens elements is decreased in order to reduce the thicknesses of the lens groups, the number of lens elements constituting a focusing lens group is decreased accordingly. As a result, it becomes difficult to suitably correct aberrations from infinity to the closest photographing position with respect to any focal length points in an entire zooming range determined by the short focal length extremity and the long focal length extremity. This tendency becomes more remarkable when the zoom ratio is set higher. In order to correct aberrations suitably from infinity to the closest photographing position, the number of lens elements in the focusing lens group has to be increased, and therefore miniaturization of the three-lens-group zoom lens system cannot be achieved.